The invention relates to a method of producing a metal matrix which can be used in the manufacture of optically readable synthetic resin information carriers.
Such a method is, for example, disclosed in Applicants United Kingdom Patent Specification No. 2,128,206 (PHN 10,790). In said prior art procedure the starting point is a master disc having a preferably glass substrate and a photoresist layer in which an optically readable information track is provided. At the side carrying the photoresist layer the master disc is coated with a layer of silver which is applied electrolessly, for example by means of a vapour deposition process, a sputtering process or a chemical plating process. On top of this layer a metal peel, for example a nickel peel, is applied by means of electro-plating. The master disc is thereafter removed. The metal copy obtained which contains the silver layer is denoted the father matrix. Consequently, the father matrix is provided with a (negative) impression of the information track present in the master disc. By means of an electro-plating process a further metal copy (or replica), the what is commonly referred to as the mother disc is produced from the father matrix. For that purpose the silver layer is usually first removed from the father matrix with an oxidising agent, and the exposed nickel surface is passivated by treatment in an alkaline medium. This achieves that the mother disc can easily be removed from the father matrix. The mother disc has a positive impression of the information track present in the master disc. After its surface has been passivated, the what are commonly denoted son matrices can be produced from the mother disc by means of electro-deposition, which are used as dies in the process for the manufacture of synthetic resin information carriers. A suitable procedure is an injection moulding or injection pressing procedure. The synthetic resin information carriers obtained, such as compact disc (T.M.) or laser vision (T.M.) have an optical information track which is a positive impression of the information track of the master disc.
The prior art method described in the foregoing has the disadvantage that the quality of the master disc coated with a silver layer deteriorates or its durability is limited. The silver is easily attacked by the atmosphere, sulphides then being formed. This implies that the finished master disc must be further treated directly or very soon into a die.